1. Field of the Invention
The present invention relates to a push button switch device, which is a control switch installed in the instrument panel of an automobile or the like, and which is equipped with a backlight function that allows the operation position and operation state to be identified so as to facilitate nighttime operation.
2. Description of the Related Art
Some of the push button switches that are installed in automobiles, consumer electronics, and so forth are provided with a light for illuminating the switch so that it can be found in the dark, such as at night, and with a light for displaying the operational state, with these lights provided next to each other. Since lights having different meanings come on at locations that are very close together, if there is any light leakage between the two it can lead to a misreading of the information, and there has been a need for a switch structure that is free of light leakage. The present applicant has previously manufactured the push button automobile heater control switch shown in FIG. 5. This switch is what is known as a push-push switch; when the driver pushes a control knob 1, a slide contact 5 moves and the switch is turned on and held in this depressed position. When the driver again pushes the control knob 1, the switch is turned off and the control knob 1 is returned by a spring 6 to its original position. 2′ in FIG. 5 is a miniature lamp used for nighttime illumination, so that the location of the switch can be found even in the dark. 3′ is another miniature lamp, which tells the driver whether the switch is on or off. This lamp is lit when the control knob 1 is pushed and the switch is turned on, and is extinguished with the control knob 1 is again pushed and returns to its home (off) position. The light from the lamp 3′ indicating whether the switch is on or off goes through a light transmitting member 7 and reaches the surface of the control knob 1. In contrast, when the nighttime illumination lamp 2′ is lit, its light shines directly on the back of the control knob 1 and lights up a wide area of the surface. In order for the driver to be able to distinguish between these two lights, the space on the back side of the control knob 1 is such that the region in which the light transmitting member 7 is disposed is completely isolated by a light barrier 4.
This conventional switch employed miniature lamps as the light source for both nighttime illumination and operational display, but there has been demand for replacing these with LEDs because the latter last longer and consume less power, and switch design has already begun moving in that direction. When LEDs are employed in place of conventional miniature light bulbs, connecting and attaching the terminals of the various LEDs in small divided spaces entails a lot of work, so it is preferable to use a structure in which the LEDs are all attached to a single substrate ahead of time and then incorporated into the switch. Also, the miniature light bulbs of conventional devices were installed from a direction perpendicular to the direction in which the switch was depressed, but the installation conditions of peripheral devices can require installation in the operational axis direction, and the substrate has to be in a perpendicular relationship with the operational axis. However, if this type of push button switch has movable parts, and two LEDs are disposed on a substrate perpendicular to the operational axis, then a light barrier that blocks the light from these LEDs also has to have a movable structure.
An invention titled “Push Button Switch,” published as Japanese Laid-Open Patent Application H8-64062 and disclosed in Japan on Mar. 8, 1996, is a push button switch that employs an LED for its light source, and presents a structure in which light leaks between adjacent switches. The top drawing in FIG. 6 is a front view thereof, the lower left drawing is the right portion of a cross section along the B-B line, and the lower right drawing is an enlarged view of the light blocking structure of the control button. This switch operates as follows. When a control button 13 is operated to turn on a switch fixed on a printed substrate 18, an LED fixed to this printed substrate 18 is lit, and the function corresponding to the control button 13 is also performed. When a bulb 17 provided for nighttime illumination on the printed substrate 18 is lit, the light emitted from the bulb 17, other than the portion that illuminates a display component 10a, is reflected by the inner walls of the housing and other parts, and is guided to a gap D leading to the adjacent control button 13. A rib 13b for preventing light leakage is provided as a protruding component to this portion of one control button 13, and the adjacent control button 13 is provided with a step 13c for preventing light leakage by ensuring enough distance from this light blocking rib 13b to permit the depression displacement of the switch, so these block bulb light and prevent the leakage of this light. The result of this is that each of the control buttons 13 stands out more distinctly. Nevertheless, because there is a stepped gap with this structure, the rib 13b for preventing light leakage and the step 13c for preventing light leakage presented here are unable to block the light completely because of the scattered reflection of the light.